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The lackluster military spending of European countries has been a source of constant complaint for U.S. officials in recent years. Yet most of Washington’s demands for action have lacked credibility, since no U.S. administration has ever penalized a European state for slacking on defense. Instead, U.S. officials have typically sought to reassure allies, in Europe and elsewhere, that the United States would do whatever was necessary to protect them.

The United States’ allies fear that U.S. President Donald Trump may take a different course. Trump spared no criticism during his campaign for Washington’s partners in East Asia, Europe, and the Middle East, suggesting that some of the United States’ security commitments were obsolete and that foreign countries had been reaping the benefits of U.S. protection without providing much in return. Foreign observers variously worried that Trump might send allied states a bill for the upkeep of U.S. forces, withdraw troops to the United States, or refuse to defend their countries from foreign aggression.

Since then, foreign officials have been watching Trump’s appointments, attempting to discern what the new president might demand of U.S. allies. Both Rex Tillerson, Trump’s pick for secretary of state, and Secretary of Defense James Mattis sounded reassuring during their confirmation hearings. The former called NATO’s Article 5 guarantee “inviolable,” and the latter stated that “NATO is vital to our interests.”

ANDREW WINNING / REUTERS

NATO leaders watch a fly-past at a summit near Newport, Wales, September 2014.

Still, U.S. allies have reason for concern. Europeans can point to small upticks in military spending this year, but that increase looks significant only when compared with years of substantial reductions, and no major enhancements to the combat capabilities of Europe’s militaries seem to be in the offing. As for South Korea, two weeks after the election, Chang Myoung-jin, the head of the country’s Defense Acquisition Program Administration, said that his government would “inevitably have to” embrace U.S.